In recent years, with the growing popularity of the bicycle, there has come to be a greater demand for and usage of bicycles operating on the variable ratio power drive principle commonly called the derailleur drive. Basically, this principle allows for changing the ratio of sprocket gears as between the forward drive sprocket (operated by foot pedal power) and the rear multiple cluster of sprocket gears laterally placed one to the other with a variety of diameters. A mechanism is provided whereby the drive chain may be derailed at the rear cluster from one sprocket gear to the next. Some of these systems also provide for sprocket gear change at the forward sprocket.
These bicycle derailleur gear shifting mechanisms in the prior art have presented a series of problems in actual operation such as the following:
1. The inability of the operator to position the bicycle drive chain precisely in line with a selected sprocket gear of the rear sprocket cluster for the purpose of derailing the drive chain to the selected sprocket when effecting a gear change.
2. The inability of the operator to recognize whether or not the bicycle drive is accurately positioned after the gear change is effected, as there still may be some offset.
3. The awkward and potentially dangerous utilization of auxiliary gear shifting levers which are generally located remote from the handlebar grips and which require the operator to release his hold on the handlebar grip steering mechanism in order to operate the gear-shifting lever.
The mechanism of the present invention overcomes the problems posed by prior art devices and the problems enumerated above. The gear-shifting apparatus disclosed herein provides for more positive, more precise, and more effective control of the derailing and shifting of the bicycle drive chain by either mechanical, electromechanical, hydraulic or other means. For example, electromechanical control can enable finger-tip push-button gear changing without necessitating the removal of either hand from the handlebar (as in the prior art) to shift a gear shift lever located remotely from the handlebar grip. Further, this mechanism is an improvement over that described in the aforementioned U.S. Pat. No. 3,863,512 in that no operator judgement is necessary as to when to terminate the shifting operation. When the gear-ratio shift has been accomplished, the electrical contact sensors and the control circuitry automatically shut off the shift operation. The operator has merely to depress one end (or the other) of a rocker switch to initiate the shift and nothing more, as the shut-off occurs automatically.
The disclosure of the present invention describes an idler assembly mechanism for attachment adjacent to the rear multiple sprocket gear cluster wherein simple positive means are provided for shifting the drive chain from any sprocket gear to any other desired sprocket gear quickly, positively and without offset or uncertainty. The described idler assembly mechanism is a unit within itself having an activating means which may be activated through electrical switches which are controlled by the operator near the steering mechanism, that is, the handlebars adjacent the operator's fingertips.